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hyphyp
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Merge pull request #1282 from vedantk/cherry
[LiveDebugValues] Add cutoffs to avoid pathological behavior
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‎llvm/lib/CodeGen/LiveDebugValues.cpp‎

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Original file line numberDiff line numberDiff line change
@@ -80,6 +80,18 @@ using namespace llvm;
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STATISTIC(NumInserted, "Number of DBG_VALUE instructions inserted");
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STATISTIC(NumRemoved, "Number of DBG_VALUE instructions removed");
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// Options to prevent pathological compile-time behavior. If InputBBLimit and
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// InputDbgValueLimit are both exceeded, range extension is disabled.
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static cl::opt<unsigned> InputBBLimit(
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"livedebugvalues-input-bb-limit",
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cl::desc("Maximum input basic blocks before DBG_VALUE limit applies"),
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cl::init(10000), cl::Hidden);
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static cl::opt<unsigned> InputDbgValueLimit(
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"livedebugvalues-input-dbg-value-limit",
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cl::desc(
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"Maximum input DBG_VALUE insts supported by debug range extension"),
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cl::init(50000), cl::Hidden);
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// If @MI is a DBG_VALUE with debug value described by a defined
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// register, returns the number of this register. In the other case, returns 0.
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static Register isDbgValueDescribedByReg(const MachineInstr &MI) {
@@ -1752,6 +1764,22 @@ bool LiveDebugValues::ExtendRanges(MachineFunction &MF) {
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Worklist.push(RPONumber);
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++RPONumber;
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}
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if (RPONumber > InputBBLimit) {
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unsigned NumInputDbgValues = 0;
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for (auto &MBB : MF)
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for (auto &MI : MBB)
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if (MI.isDebugValue())
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++NumInputDbgValues;
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if (NumInputDbgValues > InputDbgValueLimit) {
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LLVM_DEBUG(dbgs() << "Disabling LiveDebugValues: " << MF.getName()
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<< " has " << RPONumber << " basic blocks and "
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<< NumInputDbgValues
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<< " input DBG_VALUEs, exceeding limits.\n");
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return false;
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}
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}
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// This is a standard "union of predecessor outs" dataflow problem.
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// To solve it, we perform join() and process() using the two worklist method
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// until the ranges converge.

‎llvm/test/DebugInfo/MIR/X86/live-debug-values-cutoffs.mir‎

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@@ -0,0 +1,99 @@
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# Test cutoffs for livedebugvalues debug range extension.
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# Disable LDV if the input-bb-limit AND the input-dbg-value-limit are both exceeded.
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# RUN: llc %s -o - -run-pass=livedebugvalues -mtriple=x86_64-unknown-unknown \
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# RUN: -livedebugvalues-input-bb-limit=1 \
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# RUN: -livedebugvalues-input-dbg-value-limit=1 \
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# RUN: | FileCheck %s -check-prefix=LDV-DISABLED
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# RUN: llc %s -o - -run-pass=livedebugvalues -mtriple=x86_64-unknown-unknown \
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# RUN: -livedebugvalues-input-bb-limit=1 \
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# RUN: -livedebugvalues-input-dbg-value-limit=10 \
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# RUN: | FileCheck %s -check-prefix=LDV-ENABLED
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# RUN: llc %s -o - -run-pass=livedebugvalues -mtriple=x86_64-unknown-unknown \
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# RUN: -livedebugvalues-input-bb-limit=10 \
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# RUN: -livedebugvalues-input-dbg-value-limit=1 \
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# RUN: | FileCheck %s -check-prefix=LDV-ENABLED
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# RUN: llc %s -o - -run-pass=livedebugvalues -mtriple=x86_64-unknown-unknown \
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# RUN: -livedebugvalues-input-bb-limit=10 \
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# RUN: -livedebugvalues-input-dbg-value-limit=10 \
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# RUN: | FileCheck %s -check-prefix=LDV-ENABLED
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# LDV-DISABLED-LABEL: bb.1.exit
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# LDV-DISABLED-NEXT: $edi = MOV32rm
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# LDV-ENABLED-LABEL: bb.1.exit
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# LDV-ENABLED-NEXT: DBG_VALUE $rsp, 0, {{.*}}, !DIExpression(DW_OP_plus_uconst, 4)
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# LDV-ENABLED-NEXT: $edi = MOV32rm
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--- |
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target datalayout = "e-m:o-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
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declare i32 @use(i32)
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define i32 @foo(i32 %x) !dbg !6 {
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entry:
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%y = add i32 %x, %x, !dbg !12
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call void @llvm.dbg.value(metadata i32 %y, metadata !9, metadata !DIExpression()), !dbg !12
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br label %exit, !dbg !13
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exit: ; preds = %entry
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%z = call i32 @use(i32 %y), !dbg !14
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call void @llvm.dbg.value(metadata i32 %z, metadata !11, metadata !DIExpression()), !dbg !14
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ret i32 %z, !dbg !15
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}
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declare void @llvm.dbg.value(metadata, metadata, metadata)
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!llvm.dbg.cu = !{!0}
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!llvm.debugify = !{!3, !4}
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!llvm.module.flags = !{!5}
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!0 = distinct !DICompileUnit(language: DW_LANG_C, file: !1, producer: "debugify", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
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!1 = !DIFile(filename: "/tmp/t.ll", directory: "/")
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!2 = !{}
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!3 = !{i32 4}
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!4 = !{i32 2}
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!5 = !{i32 2, !"Debug Info Version", i32 3}
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!6 = distinct !DISubprogram(name: "foo", linkageName: "foo", scope: null, file: !1, line: 1, type: !7, scopeLine: 1, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !8)
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!7 = !DISubroutineType(types: !2)
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!8 = !{!9, !11}
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!9 = !DILocalVariable(name: "1", scope: !6, file: !1, line: 1, type: !10)
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!10 = !DIBasicType(name: "ty32", size: 32, encoding: DW_ATE_unsigned)
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!11 = !DILocalVariable(name: "2", scope: !6, file: !1, line: 3, type: !10)
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!12 = !DILocation(line: 1, column: 1, scope: !6)
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!13 = !DILocation(line: 2, column: 1, scope: !6)
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!14 = !DILocation(line: 3, column: 1, scope: !6)
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!15 = !DILocation(line: 4, column: 1, scope: !6)
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...
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---
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name: foo
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liveins:
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- { reg: '$edi', virtual-reg: '' }
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stack:
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- { id: 0, name: '', type: spill-slot, offset: -12, size: 4, alignment: 4,
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stack-id: default, callee-saved-register: '', callee-saved-restored: true,
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debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
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body: |
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bb.0.entry:
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successors: %bb.1(0x80000000)
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liveins: $edi
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frame-setup PUSH64r undef $rax, implicit-def $rsp, implicit $rsp
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CFI_INSTRUCTION def_cfa_offset 16
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renamable $edi = ADD32rr renamable $edi, killed renamable $edi, implicit-def $eflags, debug-location !12
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DBG_VALUE renamable $edi, $noreg, !9, !DIExpression(), debug-location !12
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MOV32mr $rsp, 1, $noreg, 4, $noreg, killed $edi :: (store 4 into %stack.0)
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DBG_VALUE $rsp, 0, !9, !DIExpression(DW_OP_plus_uconst, 4), debug-location !12
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bb.1.exit:
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$edi = MOV32rm $rsp, 1, $noreg, 4, $noreg :: (load 4 from %stack.0)
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CALL64pcrel32 @use, csr_64, implicit $rsp, implicit $ssp, implicit killed $edi, implicit-def $eax, debug-location !14
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DBG_VALUE renamable $eax, $noreg, !11, !DIExpression(), debug-location !14
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$rcx = frame-destroy POP64r implicit-def $rsp, implicit $rsp, debug-location !15
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RETQ implicit killed $eax, debug-location !15
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...

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